“On cell” is the technology that embeds a touch screen between a color filter glass and a polarizer; i.e., touch sensors are arranged on the LCD panel, the driving channels (Tx) and the inducing channels (Rx) are formed with single layer ITO, these two groups of electrodes respectively constituting two poles of a capacitor. When a finger touches the capacitive screen, the coupling between two electrodes near the touch point is affected, thereby changing the capacitance between these two electrodes; in the detection of the mutual capacitance, excitation signals are output from the electrodes in the horizontal direction in turn, all the electrodes in the vertical direction receive signals at the same time; in such a manner, the capacitance values for all the intersection points of the horizontal and vertical electrodes (i.e., the capacitance values for the two-dimensional plane of the whole touch screen) can be obtained. When the finger is close to the touch screen, local capacitance can be reduced; based on the variation data of two-dimensional capacitance of the touch screen, the coordinates of each touch point can be calculated. Thus, even if there are multiple touch points on the screen, the real coordinates of each touch point can be calculated.
However, the impact on the product appearance and performance due to the shadow elimination is an important problem for the SLOC touch screen (in which the touch control material is located over the color filter glass within the LCD layer). In the traditional production structure of the touch screen, there is a reflectivity difference between the ITO pattern region and the non ITO region, therefore the etching marks on the ITO is clearly visible under conventional environment and strong light. In addition, the smoothness of the glass surface is reduced after thinning process, resulting in poor flatness of the ITO film, further increasing the phenomenon of shadow; meanwhile, ITO defects can cause short circuit between the channels, resulting in more defects.
The shadow elimination process for a conventional On Cell product comprises:
1) firstly depositing a layer of silicon dioxide film on a glass substrate as a basal layer with the approach of vacuum magnetron continuous plating; then, depositing a layer of indium tin oxide film on the silicon dioxide film as a conductive film layer by magnetron sputtering; finally, plating a layer of silicon nitride film on the indium tin oxide film as a shadow elimination layer; however, plating a silicon nitride film needs high-temperature film-forming, which is apt to cause bubble problem;
2) firstly plating niobium pentoxide (Nb2O5) on a glass substrate by magnetron sputtering, forming a niobium pentoxide layer as a shadow elimination layer; then coating a silicon dioxide layer; finally coating a indium tin oxide layer and observing the effect of shadow elimination. The structure is glass+Nb2O5+SiO2+ITO; in this way, during the production of capacitive touch screen, the square resistance value of indium tin oxide should be in a predetermined range, and the shadow elimination effect should also be ensured. Therefore, after plating niobium pentoxide, the square resistance value of indium tin oxide should be fine tuned to obtain a good shadow elimination effect. With this arrangement, when the shadow elimination effect is qualified, the square resistance value of indium tin oxide may not be up to the standard; or, when the square resistance value of indium tin oxide is up to the standard, the shadow elimination effect may not be qualified. Therefore, the above mentioned process can not give consideration to the square resistance value of indium tin oxide and the shadow elimination effect, the yield being low; it is difficult to meet the market demand.